Technical Field
The present invention relates to a novel derivative of pyrroloquinoline quinone represented by the following formula (1).

Background Art
Pyrroloquinoline quinone (hereinafter, also referred to as “PQQ”) has been suggested to have a possibility of a new vitamin, and has been attracted as a substance useful for health supplements and cosmetics. Moreover, PQQ exists in not only bacteria but eukaryotes such as fungus and yeast, and performs important functions as a coenzyme. Furthermore, until recent years, PQQ had been clarified to have many physiological activities such as a cell growth promotion effect, an anticataract effect, a liver disorder preventive care effect, a wound healing effect, an anti-allergic effect, a reverse-transcriptase inhibiting effect, and a glyoxalase I inhibiting effect-anticancer effect.
This PQQ has an absorption in a visible part. Therefore, a free body and an alkali metal salt of PQQ are a solid or a solution having a color between red and dark red (for example, refer to Non Patent Document 1, 2, and 3).
As a PQQ derivative, for example, an esterified derivative obtained by reacting a carboxylic acid in PQQ with an alcohol has been reported (for example, refer to Non Patent Document 2 and 4).
On the other hand, a composition containing PQQ and an alcohol has been reported so far (for example, refer to Patent Document 1). In addition, as a reaction product of PQQ and an alcohol, a carboxylic acid ester of PQQ and a hemiacetal form to which an alcohol is further added have been reported (for example, refer to Non Patent Document 5).